When travelling on a Melbourne tram, you might have noticed a little window of sand next to your seat. So what’s the story?
@yarratrams I've always wondered about those little windows of sand on trams. What is the sand for? Why is there a window to it?
— Jessica (@jessvanc) July 26, 2012
Steel wheels rolling on steel rails might be a low friction surface for moving along efficiently, but when it is time to stop, a tram needs all of the friction it can get – and dropping sand onto the track is the easiest way to achieve it.
The story of sand on trams starts at the depot, where trucks deliver clean sand into a tall tower.
Hoppers onboard each tram carry the sand, which are refilled when required.
Transported via buggy.
Customised wheelbarrows.
Or pneumatic pipes.
Little windows inside the tram allow the sand level to be checked.
Inside the driver’s cab, there is a button to drop sand.
When pushed, the pipes from the hoppers open, dropping sand onto the tracks just in front of the wheels.
As well as giving extra friction between the tram wheels and the rails, sand also serves as an electrical insulator – an unwanted attribute that results in electrical arcing when too much builds up on the tracks.
The sand also ends up in the flangways of the rails, making a mess.
To prevent this, Yarra Trams has a fleet of modified street sweepers to vacuum the sand back up again.
Unlike a normal street sweeper, the tram track cleaner has a special attachment to get the last bits of sand of the rail flanges.
Unfortunately the circle of sand isn’t a complete one, as the recovered grit can’t be reused in trams – specially filtered and dried sand is required, or the hoppers and pipes get clogged up.
Further reading
- Why does wet weather stuff the trams up? – sand from a tram driver’s perspective
- Dirty tracks turning Yarra Trams into death traps – electrical hazards due to dirt and sand
- TramStore21 Report: Sanding – more about sand and tram depots
Great post Marcus! I’ve always wondered about this.
I’m glad you got something out of this post. 😀
I wonder if YT have investigated using the same conductive sand-compound as the Metro Siemens fleet?
“Conductive sand-compound” I must say that’s one fancy way to put it.
I can’t speak for YT or any other locomotive servicing companies which operate in Victoria.
But the sand which MTM uses for the Siemens fleet is just ordinary fine, washed Silica Sand commonly used as Foundary Sand, Grout and in this case adhesive purposes.
Comes from a company called Rocla, mined and processed locally at the Langwarrin plant, according to the MSDS the contents is >98% crystalline silica (quartz) and <2% mineral and organic impurities, nothing magical really.
Over in Britain they do use a mix of sand, aluminium and adhesive on their tracks:
http://en.wikipedia.org/wiki/Sandite
However unlike sand, Sandite is applied directly to the rails by special trains – not dropped as required.
Apparently that sand as grit is a great contributor to dust in the inner city, and blackening of buildings, though not entirely convinced now that I think about it.
And I believe that the newer trams, that is all the light rail extra long ones from that last 10 years at least dont use sand, but electro-magnetic brakes. I think.
On a dry day passing trams kick up the dust, so the sand does get around.
As for the brakes on Melbourne trams, they all use three systems:
– dynamic braking, where the traction motors are used as generators to slow the tram
– disc brakes, that work just like a car by stopping the wheels
– track braking, where an electromagnet is dropped down to the rails to cause friction
The systems work together depending on the speed of the tram, and how hard the brake pedal / lever is pushed:
http://www.transport.vic.gov.au/__data/assets/pdf_file/0003/30954/Tram-to-Tram-Collision-St-Kilda-Road-near-Commercial-Road-Melbourne-31-Jan-2009_1.pdf
http://www.transport.vic.gov.au/__data/assets/word_doc/0011/83567/Tram-Collision-St-Kilda-Rd-and-Leopold-Streets-Melbourne-24-Sep-2007.DOC
Thank you Marcus and other contributors. That was very informative.
Just to be clear for Rohan’s benefit, all Melbourne trams use sand.
My photo showing the window into the sandbox is onboard a 2003-era D2 class low floor tram.